1. Field of the Invention
The present invention relates to filter apparatus, and more particularly to a filter having a bed comprised of multiple separated filter medias that is permitted to expand during a backwash cleaning operation.
2. The Prior Art
Filters provided with multiple loose particulate medias such as sand, crushed stone, anthracite, carbon, diatomaceous earth and other suitable materials known in the art, have been utilized in industry for decades. Problems commonly associated with filters of this type are cleaning of the filter bed and separation of the filter medias. Various solutions to these problems have been described in the prior art as discussed below.
In U.S. Pat. No. 356,819, granular filter material is packed in a diaphragm having wire cloth on both sides. The diaphragm is then cemented to the inside walls of the filter to prevent it from moving in response to the current passing through the filter. This diaphragm arrangement prevents loss of the filter media. The diaphragms are individually cleaned when necessary.
U.S. Pat. No. 651,948 describes a water filter containing asbestos, charcoal and sand with partitions therebetween. A water tight seal is provided between the partitions and the filter wall. The invention provides for physically removing the partition and medias for cleaning purposes.
An anthracite and sand filter is described in U.S. Pat. No. 3,436,260. This filter is utilized in cane sugar refining. It is cleaned by backwashing with water and "scouring gas." The filter is not provided with a separator between the anthracite and sand.
British Pat. Nos. 3390 and 2557 also describe filters having sand and carbn media. In the 3390 patent, filtering plates are provided which can be removed for replacement or cleaning. The sand or charcoal is packed in an envelope that forms a part of the plate. The 2557 patent describes a filter having a perforated false bottom and a movable hinged top which can be opened for cleaning purposes.
The present invention is an improvement in filter apparatus which provides for separation of multiple filter medias and allows expansion of the filter bed during a backwash cleaning operation.